Fulvio D’Acquisto at Queen Mary University of London and his colleagues studied mice missing a recombinant activating gene (RAG), which controls the development of immune cells. Without it, mice lack a working immune system and some genes are expressed differently, including those involved in the olfactory system. “That rang bells, because people with immune deficiencies often lose their sense of smell,” says D’Acquisto.

His team measured how long it took mice to find chocolate chip cookies buried in their cages. Those missing RAG took five times as long as normal mice, and failed to respond to other scents. Further study uncovered abnormalities in the lining of their noses (Frontiers in Neuroscience, doi.org/8vm).

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D’Acquisto suspects olfactory cell survival might hinge on the presence of some factor released by immune cells. There could be an evolutionary benefit&colon; “If you have a problem with the immune system, it would be a good idea to avoid exposing yourself to danger,” D’Acquisto says. “Not smelling properly could encourage you to stay still.”

This article appeared in print under the headline “Feeling unwell, and lost your sense of smell?”